Accurate in vivo measurement of tibiofemoral force is important in total knee arthroplasty as this determines polyethylene stresses and cold flow, stress distribution in the implant, and stress transfer to the underlying implant bone interface. Theoretic estimates of tibiofemoral forces have varied widely depending on the mathematical models used. The six-degree of freedom of motion, complex articular surface topography, changing joint contact position, intra- and extra-articular ligaments, number of muscles crossing the knee joint and the presence of the patellofemoral joint contribute to the difficulty in developing reliable models of the knee. The purpose of this developmental research grant is to design, manufacture and test an instrumented total knee replacement tibial prosthesis that accurately measures all six components of tibial forces in vivo after total knee arthroplasty. [unreadable] These will be accomplished under the following Specific Aims. Aim 1) Design and develop a prototype total knee arthroplasty tibial component instrumented with strain gauges and a telemetry system. Aim 2) In vitro cadaver testing to demonstrate accuracy, feasibility, and integrity of telemetry link. Aim 3) Trial intraoperative implantation. This device can be used to validate existing models of the knee that estimate these forces or to develop more accurate models. In conjunction with kinematic data, accurate tibiofemoral force data may be used to design more effective knee testing rigs and wear simulators. Additional uses are intraoperative measurement of forces to determine soft tissue balancing, evaluation of the effects of rehabilitation, external bracing, and athletic activities, and activities of daily living. [unreadable] [unreadable]